The Bureau of Mines conducted research to simulate in situ leaching of a porphyry copper sulfide ore. The purpose was to determine the effects on copper leaching of additions of nacl to a conventional sulfate leach system and to analyze the oxidant requirements and the oxidation products that resulted from leaching of the sulfide minerals in the ore. Baseline sulfate and sulfate plus 2-pct-nacl- leach-solution experiments employing 167-kg (367-lb) and 152-kg (333- lb) charges, respectively, were conducted. The minus 25.4-Cm (10- inch) ore was leached at 90 deg c under flooded conditions with 2.8 Mpa (400 psig) of oxygen bubbling through the system. Sixty-seven pct of the copper was extracted in 1,236 days of leaching in the nacl experiment, whereas 47 pct of the copper was extracted in 913 days of leaching in the baseline experiment. Diffusion into and out of the ore fragments controlled the rate of leaching, which precluded enhancement of the leach rate by the chloride ions. The calculated oxygen consumption was 3.17 Kg/kg of copper extracted in the baseline experiment and 3.46 Kg/kg of copper extracted in the experiment to determine the effect of chloride ions.